How to add a uniform complex shape to a high poly geometry?
It can be obtained with a subdivision surface modifier, starting from a simple shape:



Here we can make it using a mirror modifier on X, Y, Z. 

The base shape is as shown below: just the profile repeated/rotated at the extremities and at the corner.

With the mirror and the subdivision surface, we obtain this:



Now, refine the profile adding two loop cuts and grabbing down the border:





Edit following the comments, if you want to do it from an already modeled base shape:


In edit mode, duplicate an edge loop (note that if the subdivision is already applied on the object, that's changing nothing)
Separate it
Convert it to curve
Give some bevel to the curve
Set the curve 'U' resolution to 1 (that will keep the same amount of vertices around as the original)
Convert back to mesh


After that, to do: remove some edges loops in the inner part in both objects, join them, and bridge edge loops between them.